Caracterização e avaliação da atividade fotocatalítica de catalisadores baseados no TiO2, sintetizados mediante hidrólise em uma mistura de solventes

This study involved the synthesis of photocatalysts based on titanium dioxide (TiO2). The photocatalysts were synthesized by the sol-gel method using three different proportions of acetone (25%, 50% and 75% v/v) in water/acetone mixtures, in order to control the hydrolysis of the precursor of titanium (titanium tetraisopropoxide). Aiming to investigate the structural, morphological and electronic changes provoked by the use of the solvent mixtures, different methodologies were used to characterize the oxides, such as X-ray diffraction (XRD), RAMAN spectroscopy, UV-Vis diffuse reflectance spectroscopy, and measurements of specific surface area (BET). XRD combined to RAMAN analyses revealed that the products are two-phase highly crystalline oxides involving anatase as main phase and brookite. Besides, the refined XRD using the method of Rietveld demonstrated that the presence of acetone during the synthesis influenced in the composition of the crystalline phases, increasing the proportion of the brookite phase between 13 and 22%. The band gap energy of these oxides practically did not suffer changes as function of the synthesis conditions. As shown by the isotherm, these photocatalysts are mesoporous materials with mean diameter of pores of 7 nm and approximately 20% of porosity. The surface area of the oxides prepared by hydrolysis in presence of acetone was 12% higher compared to the bare oxide. After characterized, these oxides had their photocatalytic activities evaluated by photodegradation of the azo dyes Ponceau 4R (P4R), Tartrazine (TTZ) and Reactive Red 120 (RR120), and also by the ability to mediate the photocatalytic production of hydrogen. Using the most efficient photocatalyst, the mineralization achieved for the dyes P4R, RR120 and TTZ was of respectively 83%, 79% and 56% in 120 minutes of reaction, while the discoloration of P4R e RR120 reached 100% and 94% for TTZ. In addition, the same photocatalyst in the presence of 0.5% w/w of Platinum and suspended in a 5:1 v/v water/methanol mixture, produced 56 mmol of gaseous hydrogen in five hours of experiment, corresponding to a specific rate of hydrogen production of 139.5 mmol h-1 g-1.Conselho Nacional de Desenvolvimento Científico e TecnológicoCoordenação de Aperfeiçoamento de Pessoal de Nível SuperiorFundação de Amparo a Pesquisa do Estado de Minas GeraisDissertação (Mestrado)O presente estudo envolveu a síntese de fotocatalisadores baseados no dióxido de titânio (TiO2), utilizando acetona para controlar a hidrólise do precursor de titânio empregado (tetraisopropóxido de titânio). Os fotocatalisadores foram sintetizados pelo método sol-gel, utilizando diferentes misturas de água/acetona (25%, 50%, 75% v/v de acetona) na hidrólise do precursor de titânio. Com a finalidade de investigar as mudanças estruturais, morfológicas e eletrônicas provocadas pelo uso da mistura água/acetona, foram empregadas diferentes técnicas de caracterização, incluindo difração de raios-X(DRX), espectroscopia RAMAN, espectroscopia por reflectância difusa no UV-Vis e medidas de área superficial específica (BET). As análises de raios-X junto à espectroscopia RAMAN revelaram óxidos altamente cristalinos com a coexistência das fases anatase, como fase principal, e broquita como fase secundária. Além disso, os difratogramas refinados pelo método Rietveld demonstraram que a presença de acetona durante a síntese interferiu na composição das fases cristalinas, aumentando a proporção da fase broquita entre 13 e 22%. A energia de band gap dos óxidos sintetizados praticamente não sofreu alteração em função das condições de síntese. Conforme apresentado pelas isotermas, os fotocatalisadores sintetizados são materiais mesoporosos com diâmetro médio de poros de 7 nm e aproximadamente 20% de porosidade. A área superficial dos óxidos provenientes da hidrólise feita com acetona aumentou em cerca de 12% em relação ao óxido padrão. Depois de caracterizados, o potencial fotocatalítico dos óxidos foi avaliado através da fotodegradação dos azocorantes Ponceau 4R (P4R), Tartrazina (TTZ) e Reactive Red 120 (RR120), e também através da produção fotocatalítica de hidrogênio. Com o fotocatalisador mais eficiente alcançou-se respectivamente 83%, 79% e 56% de mineralização dos corantes P4R, RR120 e TTZ em 120 minutos de reação. Já a descoloração foi de 100% para o P4R e RR120 e de 94% para a TTZ. O mesmo óxido carregado com 0,5% de Platina (Pt) e suspenso a uma mistura água/metanol 5:1 v/v, produziu aproximadamente 56 mmol de hidrogênio gasoso em cinco horas de experimento, correspondendo a uma taxa específica de produção de hidrogênio de 139,5 mmol h-1 g-1

Synthesis and Evaluation of the Photocatalytic Activity of Nanostructured Composites Based on SiO2 Recovered by TiO2

Almost spherical SiO2 nanoparticles were recovered by thin films of TiO2 (highly crystalline anatase) produced in situ sol-gel syntheses. Silica coating was proven by scanning electron microscopy and infrared measurements. The outstanding photocatalytic efficiency of this material was proven by the degradation of the dye Ponceau 4R (P4R) in aqueous solution, by monitoring its discoloration as well as by the photocatalytic production of gaseous hydrogen. In the first case, the color of the solutions submitted to the photocatalytic process was reduced to zero in 140 minutes of reaction. Regarding the hydrogen production, 5.5 mmol of H2 were obtained in 5 hours of reaction, corresponding to a specific rate of production of 13.6 mmol g-1h-1, a value much higher than that obtained using TiO2 P25 (2.66 mmol g-1h-1) under similar conditions, or even with other photocatalysts reported in the literature. This outstanding photocatalytic activity is coherent with the specific surface area and porosity (respectively 70 m2/g and 15%), estimated for this material. On the other hand, this material presents noticeably superior band gap energy (Eg), 3.3 eV, when compared to the typical values found for TiO2. This small discrepancy, of 3%, may be the result of the mixture of electronic states of both materials. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1347 &nbsp

ANÁLISE DE FALHA NO CUBÍCULO DE UMA SUBESTAÇÃO LOCALIZADA EM PARACATU

Resumo: Neste artigo, uma falha ocorrida no cubículo da subestação de uma mineradora situada no município de Paracatu, noroeste de Minas Gerais, é analisada de modo que possam ser definidos, por meio de um processo inferencial, a razão para tal acontecimento e os procedimentos necessários para que futuros eventos desta natureza sejam evitados, ou pelo menos contornados de forma mais eficiente. Para isso, o estudo se fundamenta em uma análise sistemática do comportamento dos sistemas de proteção incumbidos da tarefa de eliminar a falha, assim como do contexto operacional no qual o ambiente que a proporcionou estava inserido. A partir da coleta dos dados, a falha em estudo foi esclarecida de modo a expor a forma como evoluiu até seu ápice, e a importância de uma gestão correta no que envolve o sistema elétrico mostra sua essencialidade no caso em questão. Palavras-Chave: Análise; Falha; Cubículo; Subestação

Synthesis and Evaluation of the Photocatalytic Activity of Nanostructured Composites Based on SiO2 Recovered by TiO2

Almost spherical SiO2 nanoparticles were recovered by thin films of TiO2 (highly crystalline anatase) produced in situ sol-gel syntheses. Silica coating was proven by scanning electron microscopy and infrared measurements. The outstanding photocatalytic efficiency of this material was proven by the degradation of the dye Ponceau 4R (P4R) in aqueous solution, by monitoring its discoloration as well as by the photocatalytic production of gaseous hydrogen. In the first case, the color of the solutions submitted to the photocatalytic process was reduced to zero in 140 minutes of reaction. Regarding the hydrogen production, 5.5 mmol of H2 were obtained in 5 hours of reaction, corresponding to a specific rate of production of 13.6 mmol g-1h-1, a value much higher than that obtained using TiO2 P25 (2.66 mmol g-1h-1) under similar conditions, or even with other photocatalysts reported in the literature. This outstanding photocatalytic activity is coherent with the specific surface area and porosity (respectively 70 m2/g and 15%), estimated for this material. On the other hand, this material presents noticeably superior band gap energy (Eg), 3.3 eV, when compared to the typical values found for TiO2. This small discrepancy, of 3%, may be the result of the mixture of electronic states of both materials. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1347

A classe média vai ao paraíso: representações no cinema da retomada

The article analyzes the representations of the middle class in cinema da retomada (retaken cinema), taking as examples the movies Cronicamente inviável, Salve Geral!, Carandiru e O invasor. The analyze identifies the values of this social segment, its self-image and the transposition of these cinematographic works. It has as reference the shaping of the Brazilian middle class from the 19th century, its trajectory during the 20th century and beginning of the 21st century, as well as theirs different ideological, political and social positioning.O artigo analisa as representações da classe média no cinema da retomada, tomando como exemplos os filmes Cronicamente inviável, Salve Geral!, Carandiru e O invasor. A análise identifica os valores desse segmento social, sua autoimagem e a transposição destas para as obras cinematográficas. Tem como referência a formação da classe média no Brasil a partir do século XIX, sua trajetória ao longo do século XX e início do XXI, bem como seus diferentes posicionamentos ideológicos, políticos e sociais

Determination of the Critical Micelle Concentration of Triton X-100 Using the Compound 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one as Fluorescent Probe

In the present study we estimated the Critical Micelle Concentration (CMC) of Triton X-100 in an aqueous buffered medium (PBS buffer, pH 7.4), using 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one (BDC), a push-pull compound, as extrinsic fluorescence probe. The CMC value found, 0.33 mmol L-1, shows good agreement with data from literature obtained using the fluorescence probe technique. Additionally, the polarity, in terms of the ET(30) scale, and the viscosity of the micelle microenvironment in which the probe is preferentially allocated, was estimated as being 46.9 kcal mol-1 and 70.3 cP, respectively, confirming that this microdomain is polar and highly viscous, with characteristics of polyethylene glycol groups consisting in the palisade layer at the micelle-water interface. DOI: http://dx.doi.org/10.17807/orbital.v0i0.92

Determination of the Critical Micelle Concentration of Triton X-100 Using the Compound 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one as Fluorescent Probe

In the present study we estimated the Critical Micelle Concentration (CMC) of Triton X-100 in an aqueous buffered medium (PBS buffer, pH 7.4), using 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one (BDC), a push-pull compound, as extrinsic fluorescence probe. The CMC value found, 0.33 mmol L-1, shows good agreement with data from literature obtained using the fluorescence probe technique. Additionally, the polarity, in terms of the ET(30) scale, and the viscosity of the micelle microenvironment in which the probe is preferentially allocated, was estimated as being 46.9 kcal mol-1 and 70.3 cP, respectively, confirming that this microdomain is polar and highly viscous, with characteristics of polyethylene glycol groups consisting in the palisade layer at the micelle-water interface. DOI: http://dx.doi.org/10.17807/orbital.v0i0.92